1. Field of the Invention
The present invention relates to a supercharger with an electric motor, which has an electric motor assisting a rotational drive of a compressor in a supercharger driven by an exhaust gas of an internal combustion engine and compressing an intake air so as to supercharge.
2. Description of Related Art
In order to improve a performance of an internal combustion engine, there has been widely used a supercharger (also called as “turbocharger”) driven by an exhaust gas of an internal combustion engine and compressing an intake air so as to supercharge. Further, there has been employed a supercharger with an electric motor in which an acceleration response or the like is improved by installing the electric motor on the same axis as a shaft of the supercharger and assisting a rotational drive of a compressor in an accelerated manner.
The following patent document 1 discloses a prior art relating to the supercharger with the electric motor. FIG. 1 is a cross sectional view showing a structure of a supercharger 50 with an electric motor disclosed in the patent document 1. A turbine impeller 52 and a turbine housing 51A surrounding it are arranged in an exhaust passage side of the supercharger 50. The turbine housing 51A has a scroll chamber 63 formed around the turbine impeller 52, and the scroll chamber 63 is communicated with the turbine impeller 52 via an annular gas flow path 64. Further, an exhaust port 65 coaxial with the turbine impeller 52 is formed in a center of the turbine housing 51A.
A compressor impeller 53 and a compressor housing 51B surrounding it are arranged in an intake passage side of the supercharger 50 with the electric motor. The compressor housing 51B has a scroll chamber 66 formed around the compressor impeller 53, and the scroll chamber 66 is communicated with the compressor impeller 53 via an annularly formed diffuser portion 67. Further, an intake port 68 coaxial with the compressor impeller 53 is formed in a center of the compressor housing 51C.
The turbine impeller 52 and the compressor impeller 53 are coupled by a shaft 54. The shaft 54 is rotatably supported by a bearing 55 installed in a center housing 51C. Further, in the center housing 51C, there is installed an electric motor 58 having a rotor 56 coaxially coupled to the shaft 54, and a stator 57 arranged around the rotor 56.
In the supercharger 50 with the electric motor structured as mentioned above, if an exhaust gas from an internal combustion engine is introduced to the scroll chamber 63, the exhaust gas flows to the exhaust port 65 via the annular gas flow path 64 so as to rotate the turbine impeller 52 in the process of passing through the turbine impeller 52. Accordingly, at the same time when the compressor impeller 53 coupled to the turbine impeller 52 via the shaft 54 is rotationally driven, the rotational drive is assisted by the electric motor 58, and the sucked air from the intake port is accelerated by the compressor impeller 53. The accelerated air is decelerated and pressurized in the process of passing through the diffuser portion 67 so as to be introduced to the scroll chamber 66, and is discharged from a discharge portion (not shown) so as to be supplied to the internal combustion engine.
In the supercharger 50 with the electric motor mentioned above, the electric motor 58 is rotated at a high speed during the operation of the supercharger, and is self-heated due to a windage loss and an eddy current loss. Further, since a high-temperature exhaust gas flows through the turbine, the electric motor 58 comes to a high temperature on the basis of a heat conduction from the turbine impeller 52 to the shaft 54, and from the shaft 54 to the rotor 56 of the electric motor 58. When the electric motor 58 comes to the high temperature, there are generated problems that an internal permanent magnet is demagnetized and an efficiency of the electric motor 58 is lowered. Accordingly, the supercharger in the patent document 1 is structured, as shown in FIG. 1, such that a cooling fluid flow path 60 is formed in an inner portion of a housing 51 so as to surround the electric motor 58, thereby flowing a cooling fluid 61 through the cooling fluid flow path 60 so as to cool the electric motor 58.
Regardless of whether or not the electric motor 58 mentioned above is mounted, in a motor vehicle provided with the supercharger, there is a case that the exhaust gas is flowed back to a combustion air for removing a nitrogen oxide in the exhaust gas. Further, a blow-by gas (a gas leaking to a crank chamber from a combustion chamber through a portion between a piston and a cylinder and containing an mixture) is discharged from the engine, however, there is a case that the blow-by gas is flowed back to the combustion air so as to be burnt again for reducing the air-fuel mixture discharged to the ambient air to the minimum. Accordingly, the exhaust gas, the blow-by gas or the like is contained in a part of the combustion air sucked by the supercharger. Since an oil mist of an engine oil is mixed into the exhaust gas, in the case of taking the supercharger 50 with the electric motor mentioned above as an example, the oil mist is attached to both side wall portions constituting a flow path in the process of passing through the diffuser portion 67. At this time, since the combustion air through the diffuser portion 67 is compressed and its temperature is raised, the oil mist attached to the wall portion is carbonized by a heat of the compressed air, and is stacked to be solidified. Accordingly, the solidified and stacked carbonized layer narrows the flow path of the diffuser portion 67 so as to increase a flow path resistance. Accordingly, there is a problem that it lowers a compression efficiency of the supercharger, and it causes a reduction of a reliability by extension. Further, there is a problem that the carbonized layer is peeled off due to a thermal expansion difference between the compressor housing and the carbonized layer, a vibration of the engine or the like, and there is a risk that it is sucked into the engine.
In order to solve the problem mentioned above, the following patent document 2 is disclosed as a prior art document relating to the supercharger on which the electric motor is not mounted. FIG. 2 is a cross sectional view showing a structure of a supercharger 70 disclosed in the patent document 2. As shown in FIG. 2, the supercharger 70 is structured such that the diffuser portion 67 is constituted by a diffuser flow path 67a, a seal plate 67b adjacent portion and a housing adjacent portion 67c. The seal plate 67b adjacent portion and a housing adjacent portion 67c face to each other such that the diffuser flow path 67a is arranged between them. A cooling path 72 circulating a cooling water is provided in the seal plate adjacent portion 71b. In accordance with this structure, since the cooling water is circulated in the cooling path 72, whereby the seal plate adjacent portion 67b is cooled, the oil mist is not carbonized and stacked even if the oil mist is attached to the seal plate adjacent portion 67b. In this case, in FIG. 2, the same reference numerals as those in FIG. 1 are attached to the corresponding portions to the constituting elements of the supercharger 50 with the electric motor shown in FIG. 1.
Patent Document 1:
Japanese Unexamined Patent Publication No. 2003-293785
Patent Document 2:
Japanese Unexamined Patent Publication No. 2004-44451
As mentioned above, in the supercharger on which the electric motor is not mounted, there has been proposed the technique of preventing the solidification and stack of the oil mist in the diffuser portion, however, the similar technique has not been proposed in the supercharger with the electric motor. Accordingly, in the supercharger with the electric motor, the oil mist is solidified to be stacked in the diffuser portion, and the solidified and stacked carbonized layer narrows the flow path of the diffuser portion 67 so as to increase a flow path resistance, so that there remains the problem that the compression efficiency of the supercharger is lowered.
Further, in the supercharger with the electric motor, there can be considered a matter that the solidification and stack of the oil mist in the diffuser portion 67 is prevented by arranging the similar cooling structure (the cooling path 72) to the patent document 2 mentioned above, however, in the case that the similar cooling path 72 to the patent document 2 is provided in the supercharger 50 with the electric motor in the patent document 1, it is necessary to independently arrange the cooling fluid flow path 60 and eth cooling path. Accordingly, as well as there are caused a complication of the structure, an increase of weight, an enlargement in size of the device and an increase of cost, there is a problem that an increase of weight of the vehicle is caused as a result of affecting a mounting property to the vehicle.